Cassiopeia... What do you think?

If she need a twick is in survability, and I would add this maybe with a buff of the ms boot of noxious blast, and low the animation of it, because the champ stop a lot of time using Q, and can't use the ms boot staying stopped using his skill. She needs to be able to perform his skills while she is moving.

AP ratio, except Noxious Blast that scales well late game but..I played a game with Cass once and the other team was super tanky and my twin fang couldn't do **** even with Void Staff and such..so I think they need to buff it there..and probably AP buff on Miasma..and it should give a debuff if they stand in it (relating to poison)

Her passive is good, AP ratios are great, her ult can turn team fights if used right...
Her problem is her high difficulty level, just like shaco, which is underestimated too. But this is not something to fix.